Also, if you are using the Fit Y by X platform / Bivariate platform to generate the polynomial fits, make sure to do a "Fit Special" and use uncentered polynomials. Otherwise the fitted quadratic will be of the form

f(x) = a + b*x + c*(x-xbar)

where xbar is the mean of the x values used in the regression.

Doing the fitting with a By variable and then right clicking the parameter estimates table to make a combined data table is a very efficient way to do this.